Step1: Place the manifold gasket onto the manifold making sure its the right way up! Mark the holes using your marker pen.

Step2: With the holes maked, take you centre punch and hammer and make a small pot mark in the centre of each black dot you've made. dont bother doing the ones for the corners as the bigger drill bits will just slip in to the existing hole.

Step3: take your 3mm drill bit and drill through the pot marks. then drill them again using bigger and bigger bits until you reach the 12mm. going up in steps makes it easier as you are not trying to remove lots of material at once.

Step4: the boring bit! put the manifold in a vice using some soft jaws or put cardboard around it to protect the finish. take your round file and 'elongate' the corner holes. this takes a bit but stops you breaking your wrists when the drill binds.

Step5: When you think you've filled enough, you probably haven't. but its a good idea to keep test fitting to see if you are going in the right direction
i was lucky as i have a cyclinder head in my shed so made this stage a lot easier. Once you've got it to fit it should look a bit like this:

Step6: The mounting points on the down/front pipe need to be reversed, I did this with a gas torch. heat the bend then using a suitible tool, (i chose a big set of grips, but a ring spanner would work too) slowly twist the bar through 180degrees. you could cut the welds, turn the piece around and weld it back on, but using the gas is quicker!

Step7: the Catalitic Converter, thats the only really 'custom' piece you will need to make. I used a magna flow 'High Flow' cat from the USA its a weld in one, but due to the manifold kit you will need to weld flanges on in order to make it fit the rest of the system. the flanges i had were for 2.5" pipe, whereas the cat was 3. I decided instead of just butt welding the flanges on, and guessing the centre, I'd bore out the hole and make a spigot (making the hole stepped so one side would be 2.5" and the other 3) for the cat to sit into.

To do this I put the flanges in a 4 jaw chuck on a lathe, and and slowly bored them out until i could just about push the cat into the hole. I then welded them on using a MIG welder. the spigot gives a better fit and seal agaist a butt weld.

Step8: With all the parts ready, remove all the old rusted stuff, and bolt it on in the following order:

You need to decided now wether you are going to block your EGR, the pipe that runs from the Inlet Manifold to the Exaust Manifold, if you are going to block it the car will run richer than normal, if you intend to keep the EGR open you will need to remove the pipe from the old manifold.

bolt the cat to the down/front pipe
Hang the down/front pipe using the rubber hangers
Bolt the other end of the cat to the rear of the system
Then with the down pipe resting on a jack or block of wood, bolt the manifold to it, its easier to do it whilst its below the plastic shielding on the under side of the engine bay.
lift the manifold into position with a new gasket and tighten the nuts. the two studs in the top middle of the manifold will need to be remooved and allen bolts used to replace them.